Abstract:

A method for transferring a pattern from an elastic stamp to a substrate
in the presence of a third medium is described. A proximity contact is
achieved between the stamp and the substrate. A layer of the third medium
between the stamp and the substrate is controlled to a predetermined
thickness. Stamps for carrying out this method are also described.

Claims:

1. An apparatus comprising a stamp for transferring a pattern to a
substrate in the presence of a third medium, the stamp comprising a
contact surface and drainage channels formed in the contact surface for
guiding excess third medium away from the surface of the stamp.

2. An apparatus according to claim 1 wherein the surface is patterned.

3. An apparatus of claim 1, wherein the stamp comprises an array of
protrusions.

4. An apparatus according to claim 2 wherein the patterning comprises a
micrometer sized pattern subdivided into smaller structures.

5. An apparatus according to claim 4, wherein the drainage channels extend
between the smaller structures.

6. An apparatus according to claim 1, wherein the drainage channels form a
network.

7. An apparatus comprising a stamp for transferring a pattern to a
substrate in the presence of a third medium, the stamp comprising a
permeable hydrophilic matrix for guiding excess third medium away from
the surface of the stamp.

8. An apparatus according to claim 7, wherein the stamp comprises active
vias.

9. An apparatus according to claim 8, wherein the vias are filled with a
material permeable by the third medium.

10. An apparatus according to claim 7, wherein the stamp comprises active
recesses.

11. An apparatus according to claim 10, wherein the recesses are filled
with a material permeable by the third medium.

Description:

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001]This application is a divisional of U.S. patent application Ser. No.
12/249,322, filed Oct. 10, 2008, which is a continuation of U.S. patent
application Ser. No. 10/527,277, filed Aug. 4, 2005, now U.S. Pat. No.
7,434,512, which claims priority to European Patent Application No.
02405777.0, filed 9 Sep. 2002, and all the benefits accruing therefrom
under 35 U.S.C. §119, the contents of which in its entirety are
herein incorporated by reference.

BACKGROUND

[0002]The present invention generally relates to printing and particularly
relates to methods and stamps for transferring patterns to a substrate in
the presence of a third medium.

[0003]Printing thin layers of ink or other material from a patterned
surface is well known in the printing industry. Printing processes were
originally developed for the exchange and storage of information adapted
to human vision. This typically requires pattern and overlay accuracies
down to 20 μm for acceptable reproduction. Printing processes have
been used for other forms of patterning. For example, gravure offset
printing has been used to make 50-μm-wide conductor lines on ceramic
substrates and to pattern thin-film transistors in low cost display
devices. Offset printing has been used for fabrication of capacitors and
metal conductor lines as narrow as 25 μm Additionally, printed circuit
board and integrated circuit packaging are popular applications of screen
printing in the electronics industry. See, for example, B. Michel et al.,
IBM J. Res. Develop. 45, 697 (2001) and references therein.

[0004]Another conventional printing process is known as flexography. In
flexography, a viscous ink is printed onto permeable materials such as
porous paper, permeable plastic, and the like. Flexography is a rotary
printing method involving resilient relief image plates to print images
on materials that are difficult to print on with offset or gravure
processes. Examples of such materials include cardboard, plastic films
and substrates. Flexography is therefore used widely in packaging.
Usually, the viscous ink prevents direct contact of the stamp with the
substrate because it cannot be displaced quickly enough during fast
printing operations. Transfer of a thick layer of ink is usually desired.
However, this prevents replication of small feature sizes, typically
smaller than 20 μm. See, for example, H. Kipphan, "Handbuch der
Printmedien", Springer Berlin, 2000 and J. M. Adams, D. D. Faux, and J.
J. Rieber, "Printing Technology 4th Ed.", Delamare Publishers, Albany,
N.Y.

[0005]Micro contact printing uses a similar stamp to that used in
flexography, but typically transfers a monolayer of ink onto an
impermeable surface. A more general process called soft lithography has
been applied to printing thiols and other chemicals onto a range of
surfaces. Typically, the chemicals are first applied to the stamp as
solutions in a volatile solvent or via a contact inker pad. After inking
and drying, molecules in the bulk and surface of the stamp are in a "dry"
state. The molecules are transferred by mechanical contact. The stamp is
typically formed from poly-(dimethyl)siloxane (PDMS). See, for example,
B. Michel et al. "Printing meets lithography", IBM, J. Res. Develop. 45
(5), 697 (2001)).

[0006]Micro contact processing, soft lithography, and flexography involve
locally defined, intimate contact without voids between stamp and
substrate. This is generally known as conformal contact. Conformal
contact comprises macroscopic adaptation to the shape of the substrate
and microscopic adaptation of a soft polymer layer to a rough surface.

[0007]Micro array technology is expected to accelerate genetic analysis.
Micro arrays are miniature arrays of gene fragments or proteins attached
to or deposited on glass chips. These so-called "biochips" are useful in
examining gene activity and identifying gene mutations. A hybridization
reaction is typically used between sequences on the micro array and a
fluorescent sample. In a similar manner, protein markers, viruses, and
protein expression profiles can be detected via protein specific capture
agents. After reaction, the chip is read with fluorescence detectors. The
intensity of fluorescing spots on the chip is quantified. The demand for
micro arrays and techniques for fabricating micro arrays is increasing.
Conventional methods for patterning biological molecules onto biochips
are described, for example, in M. Schena, "Micro array Biochip
Technology", Eaton Publishing, Natick Mass., (2000). In a first
conventional method, a surface is treated with compounds in a sequential
manner by: pipetting with a pipetting robot or capillary printing;
dispensing droplets with an ink jet; or, patterning with a pin spotter.
In a second conventional method, a surface is patterned with molecules in
parallel thus reducing manufacturing cost. Microfluidic networks,
capillary array printing, or micro contact processing can be employed in
implementation of the second method.

[0008]The printing of biological molecules and water soluble catalysts by
conventional techniques does not always work, is difficult to reproduce,
and results are variable. Repetitively creating homogeneous prints with
high yield over large areas is very difficult, particularly if the
molecules require permanent hydration. See, for example, A. Bernard et
al., "Micro contact Printing of Proteins", Adv. Mater. 2000 (12), 1067
(2000). Many biological molecules require at least partial hydration.
Also, many biological processes operate only when there is liquid to
provide mobility. When molecules are to selectively perform chemical
reactions on a surface in a patterned fashion, it is desirable to fix the
molecules in place to avoid blurring the pattern by spreading. In
catalytic printing therefore, it would be desirable to tether molecules
so that they can reach the surface only where desired. Limited mobility
should be permitted so that molecules can function effectively without
escaping. Biological molecules preferably encounter the substrate while
immersed in a layer of water to permit a chemisorption reaction. Because
chemisorption reactions of proteins are not selective and many potential
anchoring groups may be present on the substrate, mobility requirements
are lower. For molecule-molecule interactions, control over hydration is
desirable. One way to prevent drying without immersion in water is to
work in saturated air. In many printing operations, this is helpful.
However, the humidity level is difficult to regulate. Molecules can
interact creating adhesion detectable with an adhesion sensor as
described, for example, in EP 0 962 759 A1. For example, an antibody and
its matching antigen may interact. Similarly, a DNA oligomer may
hybridize with its complementary oligomer.

[0009]Other printing technologies include Ultra Violet (UV) lithography or
UV-molding. In such techniques, a patterned glass master is pressed into
a liquid prepolymer. The prepolymer is then cured and solidified by
exposure to UV light. See, for example, M. Colburn et al., "Patterning
nonflat substrates with a low pressure, room temperature
imprint-process", J. Vac. Sci., Technol. B. 6, 2161 (2001). On release,
the pattern formed in the polymer is a replica of the master. However, it
is difficult to displace such a polymer on large areas to achieve a
pattern with acceptable definition. There is usually a residual layer
left. Use of an identically patterned elastomeric stamp in place of glass
provides similar replication except for two differences, as follows.
Experiment indicates that in protruding areas of the stamp, where the
polymer was to be displaced down to the surface, localized dome-like
protrusions of trapped material were discovered. Secondly, variation was
observed in the thickness of features molded from the recesses in the
stamp Typically, the thickness of each feature was smaller in its center.
The depth of depression was proportional to the load applied to the
stamp. See, for example, Bietsch and Michel, "Conformal contact and
pattern stability of stamps used for soft lithography", J. Appl. Phys.
88, 4310 (2000); Johnson, "Contact Mechanics", Cambridge University
Press, Cambridge (1985); and S. P. Timoshenko and J. N. Goodier, "Theory
of Elasticity", Mc-Graw-Hill, New York). Formulae for the displacement of
liquids can be derived from lubrication theory. See, for example, A.
Cameron, "Basic Lubrication Theory" Wiley, New York (1981)).

[0010]Hydrogels are used in gel electrophoresis. Because hydrogels are
flexible, they are also used as stamp materials for printing of
biological molecules. See, for example, D. Brett et al., Langmuir 14,
3971 (1998) and Langmuir 16, 9944 (2000); M. A. Markowitz et al., Appl.
Biochem. and Biotechnol. 68, 57 (1997). Hydrogels are mainly composed of
water, and water easily diffuses through a hydrogel matrix. Thus,
hydrogels avoid hydration problems associated with PDMS based printing.
However, hydrogel stamps change volume on exposure to water or upon
drying. Also, molecules can diffuse between protrusions of the stamp.
Hydrogel stamps for parallel printing of different molecules with good
registry and separation among the spots have yet to be demonstrated.

[0011]Printing of biological molecules from an affinity stamp with
catalysts and of hydrophilic molecules from a hydrophilized PDMS stamp
onto a substrate have both been demonstrated on a research level but are
more difficult to implement commercially where areal transfer over large
surfaces is desired. The difficulty arises either because there is not
enough of the third medium required for hydration chemisorption, or
hybridization on the substrate or because there is too much third medium,
preventing intimate contact and transfer. Third medium herein is the
general expression for a medium in which other components are carried.
Depending on the application, the third medium may be a gas, water,
solvent, or polymer. See, for example, A. Bernard et al., "Affinity
capture of proteins from solution and their dissociation by contact
printing", Nature Biotechnol. 19, 866 (2001).

[0012]A third medium in the form of damping water is found in offset
printing of viscous inks onto impermeable substrates. See, for example,
J. M. Adams, D. D. Faux and J. J. Rieber, "Printing Technology 4th Ed."
Delamare Publishers, Albany, N.Y., 1996. Offset printing typically
employs a printing cylinder having a rubber printing surface. Prior to
application of ink, the surface is moistened. This transfers a thin layer
of detergent carrying water to the printing surface. The detergent
reduces surface tension in the water. The water layer covers the surface
but can be displaced by application of patterned link. A water layer
improves definition in printing processes where information on a master
is presented as a wettability pattern. The water layer prevents incursion
or adherence of ink to ink repelling regions. In transfer from the
printing surface to paper, water is absorbed into the fiber mesh of the
paper and dried. This process does not work on impermeable materials. In
such cases, the printing rubber surface slips on the water layer and the
pattern is smeared. A conventional solution to this problem is to roughen
the surface to be printed and render it hydrophilic. By controlling the
thickness of the water layer, fluid transport over large areas can be
prevented. This avoids need for capillary channels that obstruct printing
of pictures. Roughening also determines fluid resistance in percolating
channels and therefore determines printing speed. Roughening creates a
random distribution of peaks and troughs. These lead to unobstructed
percolation path between larger zones. The random process is however
inefficient because it also creates many disconnected capillary paths.

[0013]A third medium also affects high speed contact between a rigid
object and an adhesive tape in a gas such as air. The gas can build
considerable pressure between the object and the tape. The pressure
deforms the tape to create a central depression. The depression causes
trapping of an air pocket. The air pocket prevents accurate positioning
of the object in subsequent process steps such as pick and place
operation in the manufacture of semiconductor subassemblies, disk
read/write heads, and the like. Such assembly is increasingly important
as semiconductor technology moves from creating entire processors on one
chip towards assembling sub-components on intermediate carriers. To
assemble and process several chips in parallel, in flip chip bonding for
example, typically requires pre-assembly on an adhesive tape or pad.

[0014]Self-assembly of μm-sized components on a chemically patterned
surface in a third medium is typically a slow process in which particles
approach the target surface closely enough to allow specific molecular or
chemical interactions. Typically, such a process requires vigorous
agitation to provide particles with sufficient diffusion through the
third medium to establish contact with counterparts on the surface. It
can be difficult to separate the particles when the third medium is not
present. For assembly, it is desirable to have an intermediate
interaction between the parts to be assembled to better control assembly.
Appropriate placement produces stronger interaction, while inappropriate
placement provides produces weaker interaction. For faster and more
predictable assembly, an improved approach process for micrometer to
millimeter sized particles in a third medium would be desirable. The
third medium helps suspend particles that would otherwise affected by
gravitational forces.

SUMMARY

[0015]In accordance with the present invention, there is now provided a
method for transferring a pattern from an elastic stamp to a substrate in
the presence of a third medium, the method comprising: controlling a
layer of the third medium between the stamp and the substrate to a
predetermined thickness. In an exemplary embodiment of the present
invention, the substrate is rigid. In a particularly preferred embodiment
of the present invention, the substrate is impermeable. The third medium
may comprise one or more of gas, water, solvent, polymer, emulsion,
sol-gel precursor, and the like. The controlling may comprise avoiding
trapping of the third medium via the stamp matrix being permeable to the
third medium. Alternatively, the controlling may comprise forming a
nanometer sized gap in the stamp filled with the third medium.

[0016]The controlling preferably comprises providing a patterned stamp
surface having channels to drain the third medium. In a preferred
embodiment of the present invention, the controlling comprises filling
vias and recesses formed in the stamp with a component having an affinity
for the third medium. The component may be hydrophilic. The component
preferably comprises a gel. The gel is preferably swellable by the third
medium. The controlling preferably comprises swelling the gel with the
third medium to form protrusions in the stamp. In a particularly
preferred embodiment of the present invention, the controlling comprises
providing an array of protrusions and recessed zones in the stamp. The
controlling may comprise guiding excess third medium away from the
surface of the stamp via the recessed zones. The array preferably
comprises a micrometer-sized pattern subdivided into smaller structures.
The smaller structures may be separated by smaller drainage channels. The
smaller drainage channels are preferably connected to a network of larger
drainage channels. The third medium may be trapped in a shallow lens-like
pocket between the stamp and the surface of the substrate. The
controlling may comprise trapping the third medium in a pocket between
the stamp and the substrate. The stamp may comprise channels. The
channels define molecular sized gaps between the stamp and the substrate.

[0017]The present invention also extends to: use of such a method for
printing biological molecules on a surface; use of such a method for
printing dyes on a surface; use of such a method for printing catalysts
on a surface; use of such a method for printing acids or bases on a
surface; use of such a method for printing of radical initiators on a
surface; use of such a method for detection of molecules through
proximity by fluorescence resonance transfer; use of such a method for
purification and concentration of reactants; use of such a method in an
offset printing process; or use of such a method in a rolling contact
process.

[0018]Viewing the present invention from another aspect, there is now
provided a stamp for transferring a pattern to a substrate in the
presence of a third medium, the stamp comprising a contact surface and
drainage channels formed in the contact surface.

[0019]The surface is preferably patterned. The stamp may comprise an array
of protrusions. The patterning may comprise a micrometer sized pattern
subdivided into smaller structures. The drainage channels preferably
extend between the smaller structures. The drainage channels preferably
form a network.

[0020]Viewing the present invention from yet another aspect, there is now
provided a stamp for transferring a pattern to a substrate in the
presence of a third medium, the stamp comprising a permeable hydrophilic
matrix. The stamp may comprise active vias. The vias may be filled with a
material permeable by a third medium. The stamp may additionally or
alternatively comprise active recesses. The recesses may also be filled
with a material permeable by a third medium.

[0021]In a preferred embodiment of the present invention, there is
provided a method for providing controlled contact between two articles
that allows transfer with spatial control of a material from a stamp to a
substrate in the presence of a third medium. In a particularly preferred
embodiment of the present invention, there is provided a method that
allows controlled formation of nanometer sized gaps filled with the third
medium within which molecular processes can occur. In an especially
preferred embodiment of the present invention, there is provided a method
for providing conformal or proximal contact either induced by an external
force or spontaneously in self-assembly. In a preferred embodiment of the
present invention, there is provided a method wherein controlled
proximity of an article to a substrate produces patterning of the surface
with biomolecules or other molecules.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0022]Preferred embodiments of the present invention will now be
described, by way of example only, with reference to the accompanying
drawings in which:

[0023]FIG. 1A is a side view of a stamp approaching a slider bar and an
intervening viscous polymer;

[0024]FIG. 1B to 1E are graphs showing pressure as a function of lateral
position of the stamp and gap height;

[0025]FIGS. 2A to 2B are side views of a stamp approaching a substrate in
the presence of a third medium in liquid form;

[0026]FIG. 2C shows photographs of the stamp in contact with the
substrate;

[0027]FIGS. 3A to 3H are photographs of interference fringes produced by
quadrilateral patterns on the stamp when in contact with the substrate;

[0028]FIGS. 4A to 4D are cross sectional views of a stamp embodying the
present invention;

[0029]FIGS. 5A to 5F are cross-sectional and plan views of another stamp
embodying the present invention;

[0030]FIGS. 6A to 6C are cross sectional views of an adhesion sensor;

[0031]FIGS. 7A to 7D are cross sectional and plan views of yet another
stamp embodying the present invention;

[0032]FIGS. 8A and 8B are cross sectional views of stamps having shallow
channels;

[0033]FIG. 9 is a cross-sectional view of a bonding pad embodying the
present invention;

[0034]FIG. 10A is a cross sectional views of a printing cylinder;

[0035]FIG. 10B is a cross sectional view of a printing cylinder embodying
the present invention;

[0037]FIG. 11B is a side view of a printing cylinder embodying the present
invention;

[0038]FIG. 12A is a block diagram showing spontaneous interaction between
a particle and a flat surface with patterning; and,

[0039]FIG. 12B is a block diagram showing spontaneous interaction between
a particle and a flat surface without patterning;

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0040]Problems associated with printing from a stamp to a solid
impermeable substrate by conformal or proximity contact can stem from an
excess of a third medium such as a solvent. The excess prevents intimate
contact and transfer because it forms a gap between the stamp and the
substrate. The gap is filled with the excess thus preventing conformal
contact. Problems can also arise if there is a lack of third medium on
the substrate. Hydration, chemisorption and/or hybridization on the
substrate can then be adversely affected. For example, biomolecular and
chemical reactions usually require a third medium such as a solvent to
function. In the first case, it is desirable to control the amount of the
third medium to a well defined layer thickness. In a preferred embodiment
of the present invention, this is achieved by providing drainage channels
in the stamp surface. In the second case, it is desirable to offer a
controlled amount of the third medium to the substrate. In a preferred
embodiment of the present invention, this is achieved via a permeable
stamp matrix.

[0041]The physics underlying printing in the presence of a third medium
can be further understood by considering a flat stamp approaching a flat
surface. The relation between gap height h and pressure p in compressed
medium of viscosity η is described by Reynold's equation. See, for
example, A. Cameron, "Basic Lubrication Theory", Wiley (New York 1981),
Chapter 3.7. In the following example, a one-dimensional model is used.
Reynold's equation thus simplifies to:

x ( h 3 η x p ) := 12 t
h ( 1 ) ##EQU00001##

where x is the coordinate parallel to the surfaces and t is time. The
model can be applied to elongate surfaces. Examples in the data storage
field include thin film head sliders. Typical dimensions of such sliders
are 1.2 mm×50 mm. For squarer geometry, pressure may be reduced by
a factor of around 2.

[0042]If both stamp and surface are rigid, h is independent from x. The
differential equations for p and h can be solved. Thus, the origin is
chosen in the middle of the surface of width w.

p ( x ) := 3 2 P [ 1 - ( 2 x w ) 2 ] ( 2
) ##EQU00002##

[0043]FIG. 1A is a cross section of a stamp 2 and slider 4 with an
intervening third medium 8. FIG. 1B shows that the pressure profile has a
parabolic shape having a maximum in the center and dropping to zero at
the edges. The maximum is 1.5 times the mean pressure P.

[0044]In practical implementations, either the stamp 2 or the surface 4 is
elastic. The aforementioned pressure distribution causes a concave
elastic deformation in the elastic part. This can lead to pockets
trapping the third medium during contact. These trapped areas of the
third medium are referred to as "pancakes". The normal deformation can be
calculated from the pressure distribution based on a formula derived by
Bietsch and Michel in "Conformal contact and pattern stability of stamps
used for soft lithography" J. Appl. Phys. 88, 4310 (2000). For a slider
geometry, a mean pressure of 1 bar can lead to concave depressions up to
10 μm in a typical silicone elastomer having a Young's modulus of 3
MPa. The deformation scales with the Young's modulus. A harder material
reduces pancakes. In the case of slider processing, the slider 4 is rigid
and the stamp 2 is elastic.

[0045]The pressure and gap height during the approach are closely related.
There are two cases. The first case is constant applied load. The second
case is constant speed of approach.

[0046]When constant load is applied, there is a constant pressure
distribution according to equation 2. P is the mean pressure acting on
the surface 4. The gap height is then calculated from equation 1:

h := n w 2 2 P t ( 3 ) ##EQU00003##

[0047]The calculations provide an estimate of how fast the third medium 8
is displaced by the stamp 2. The third medium may be a viscous
prepolymer, gas, water, or a solvent. FIG. 1E shows decrease of gap
height for different fluids of viscosities 100 cP, 1000 cP and 10000 cP
at 1 bar applied load as a function of time. The viscosities are typical
for UV-cureable polymeric materials. A gap as small as 1 μm is
achieved for 100 cP within 1 s. However, a time of 100 s is required for
the higher viscous material of 10000 cP.

[0048]In the second case of constant approaching speed, there is
increasing pressure when the gap height is decreasing. This effect
depends on viscosity, the speed (v) and the dimension of the punch.

p := 4 n v w 2 h 3 ( 4 ) ##EQU00004##

where p is the mean pressure. FIG. 1C shows pressure as a function of gap
height for a slider, when the third medium is water and the speed of
approach is 10 μm/s. If the third medium is air, having a 60 times
lower viscosity, this diagram is true for a speed of 600 μm/s. In this
example, the pressure increases from moderate values (100 Pa) for a gap
width "w" of 10 μm to values greater than 105 Pa (=1 bar) when the gap
is reduced below 1 μm.

[0049]FIG. 1D shows how the pressure depends on the dimension of the
surface 4. At a gap width of 100 nm the pressure is reduced to 50 Pascal
for a width of the surface 4 of 1 μm compared to 50 MPa for a typical
slider geometry of 1.2 mm. The maximal pressure scales with the inverse
square of the stamp or surface size.

[0050]According to Bietsch and Michel, "Conformal contact and pattern
stability of stamps used for soft lithography" J. Appl. Phys. 88, 4310
(2000), stamps deform under constant pressure to form so called "sagging"
profiles. FIG. 2A shows an elastomeric stamp 10 approaching a rigid
surface 12 of a substrate 14 in a third medium 16, such as water. The
third medium 16 is displaced between the protruding features 18 of the
stamp 10 and the substrate 14. See the arrows in FIG. 2A. When the gap
between the stamp 10 and the substrate 14 becomes very small, the third
medium 16 cannot be displaced instantly. Pressure thus builds up with a
maximum below the center of the features 18. See the inset of FIG. 2A.
The pressure build up elastically deforms the surface 20 of the features
18. When the stamp 10 contacts with the substrate 14, a lens-like pocket
21 of the third medium is trapped below each feature 18. See FIG. 2B. The
profile follows the pressure distribution in the squeezed third medium
16. See again FIGS. 1B and 2A. FIG. 2C shows photographs of pancakes of
water between an elastic hydrophilic stamp and a rigid glass surface 22.
In this example, the stamp has square protrusions 24 of size 200 μm
molded in Sylgard® 184. The stamp was pressed onto the surface 22
with a relatively low pressure of approximately 0.05 bar. This produces a
load of 5000 Pa× fill factor, where fill factor is represented by
the contact area divided by the overall area. Interference fringes in the
form of Newton rings 24 are present. From the Newton rings 24 and the
measured refractive index of 1.3, a maximal thickness of 350 nm of
enclosed water 16 was estimated. The weak definition of the Newton rings
24 did not allow exact determination of the thickness as a function of
protrusion size. To demonstrate the effect with more definition,
experiments with UV-curable pre polymers as a third medium were
conducted. The results of these experiments are summarized in FIGS. 3A to
3H. FIGS. 3A to 3H show photographs of interference fringes on quadratic
patterns having sizes of <20, 20, 60, 100, and 200 μm, where the
term "60/20 microns" describes the width of features in μm. In FIGS.
3E and 3G, deformation of elastomeric protrusions is measured. FIGS. 3E
and 3G show the same structures as FIGS. 3F and 3H but with a larger
view. Thickness analysis as a function of pattern size showed a linear
size dependence having an intercept close to 0 and a slope of 4 nm per
μm pattern size. This shows that the enclosed layer thickness linearly
scales with pattern size. A comparison of trapped third medium and the
layer on the 200 μm square protrusions shows a difference of a factor
3. This is attributed to the viscosity difference between water and the
UV-curable prepolymer. Based on these results, a stamp for direct contact
with no water (e.g., a layer <1 nm) should have patterns with sizes
smaller than 1000 nm. On the other hand, it is also possible to choose
larger features to create gaps with defined thickness. Based on these
results, a controlled layer transfer over a gap of 4 nm, for example, can
be performed by selecting protrusions with 3 μm size, and a pattern
transfer over 20 nm can be performed by selecting protrusions with 250
μm size.

[0051]Flow resistance in fluidic networks scales with the inverse of
smallest channel dimension and with channel length. Capillary force also
scales with the inverse of channel dimensions. Fluid mechanics allows
scaling of networks to nanometer dimensions. However, patterning with
these networks is restricted by surface to volume ratio. A large surface
permits molecules dissolved in a liquid to encounter the surface and
react accordingly. This leads to depletion of the liquid. Capillary
networks are therefore very efficient in patterning via relatively short
channels with channel dimensions in the micrometer regime. See, for
example, Delamarche et al., "Microfluidic networks for chemical
patterning of substrates: Design and application to bioassays", J. Am.
Chem. Soc. 120, 500 (1998). When dimensions are in the nanometer scale,
molecules are preferably brought to desired locations by other means.
However, networks can still guide fluid to and from different zones. In
immersed systems with no liquid/air interface present, capillary forces
are immaterial. In this case, flow resistance is approximately
proportional to the product of channel length and inverse normalized
channel dimension, (w+h/(w*h))2, where w is the width and h is the
height of the channel. Scaling branched fluidic networks to the nanometer
scale involves channels with different orders of magnitude: channels with
small dimensions for short paths; channels with medium dimensions for
intermediate paths; and, channels with large dimensions for long paths.
Combining two or three layers of appropriately sized channels allows
guidance of fluids from macroscopic to nanoscopic dimensions in a
perfusion system or from nanoscopic to macroscopic dimensions in a
drainage system. This is similar to the human blood circulation system,
in which several nested subsystems are used to scale from meters in
arteries with pumped flow to nanometers in cell gaps.

[0052]Efficient biological printing and catalytic conversion involves
definition and control of a thin layer of solvent between stamp and
substrate. This is not however physically stable in conventional systems.
See, for example, A. Martin et al., "Dewetting nucleation centers at soft
interfaces", Langmuir 17, 6553 (2001), describing the spontaneous
dewetting of a meta stable liquid film on an elastomeric surface. In a
first embodiment of the present invention, this problem is solved by
avoiding the unwanted trapping of a third medium via a permeable stamp
matrix. In a second embodiment of the present invention, this problem is
solved by providing a patterned stamp surface that controls the thickness
of the third medium layer and allows excess medium to escape through
drainage channels.

[0053]In an example of the second embodiment, a layer of third medium is
trapped between a protrusion of the stamp and the substrate. The third
medium is used to carry out deposition of molecules and to provide an
environment for catalytic reactions. In a another example of the second
embodiment, patterned stamp surfaces are provided in which recesses
define molecular sized gaps. The gaps allow transfer of DNA oligomers and
polymerase chain reactions (PCR) at desired locations. In both these
examples, the target substrate is preferably within the length of the
molecule to facilitate efficient interaction.

[0054]Referring now to FIG. 4A, in an example of the first embodiment, a
stamp 26 comprises active vias 28 and recesses 30. Referring to FIG. 4B,
the vias 28 and recesses 30 are filled with a polymer gel matrix 32
permeable by a third medium, such as water or other buffer material.
Plugs are thus formed in the vias 28 and recesses 30. By uptake of the
third medium, the gel 32 swells to an equilibrium state such that the gel
32 protrudes beyond the surface 33 of the stamp 26. The swilling may be
performed in a 100% vapor phase environment. The stamp 26 may then be
stored in such an environment to prevent subsequent drying of the gel 32.
Because the gel 32 within the stamp 26 is held in another material, the
metrology of the stamp 26 is not affected by the swelling. Referring to
FIG. 4c, and particularly the arrows therein, the protrusions of gel 32
are then selectively addressed via a stencil 34 and filled with the
molecules for patterning. Each via 28 and recess 30 may be loaded with
different molecules to be transferred. Because the plugs of gel 32 in the
vias 28 and recesses 30 are isolated, there is no interdiffusion between
neighboring plugs. With a via thickness of 10 μm and a loading with
1-weight-percent of molecules, the amount of material stored in the stamp
26 is sufficient to print several hundred monolayers of molecules.
Referring to FIG. 4D, the stamp 26 is now brought into contact with a
substrate 36 to transfer the desired amount of material. The stamp 26
need not be immersed in liquid, thus reducing printing complexity. The
gel 32 holding the third medium provides full solvatation of the
molecules and also a good environment for a chemisorption reaction. The
permeability of the gel 32 allows any third medium trapped between the
stamp 26 and the substrate 36 to escape through the gel 32. This avoids
separation of stamp 26 and substrate 36 by the third medium hiking of the
different vias 28 and recesses 30 may be performed via sequential methods
such as pipetting, pin spotting, or ink jet spotting. Semi-parallel
methods based on fluidic networks may also be used to provide selective
addressing. Other examples of this embodiment may comprise only vias 28.
Similarly, further examples of this embodiment may comprise only recesses
30. There is no additional layer of third medium trapped between stamp 26
and substrate 36. However, the third medium can be in contact with the
substrate 36 as a majority component of the gel 32. Thus, the gap between
stamp 26 and the substrate 36 need not be controlled. Another application
of stamps with gel protrusions permeable by a third medium and not fully
swelled is the combined concentrating and printing of diluted solutions.
This is generally useful for detection of molecules and particularly
useful for detection of pollutants at extremely low concentrations.
Examples of pollutants include metal ions such as Pb2+, Hg2+,
Zn2+, etc. Detection can then be achieved by measuring adhesion
during removal. Other detection schemes are possible.

[0055]Referring to FIG. 5A, in an example of the second embodiment, a
hydrophilized elastomeric stamp 38 has an array of protrusions 46 with a
high fill factor. Each protrusion 46 is subdivided into smaller
protrusions 40 separated by recesses 42 acting as small channels to guide
excess third medium away before printing contact with the hydrophilic
surface 50 of a substrate 51 is established. Referring to FIG. 5B, the
smaller protrusions 40 can be circular, rectangular, or of other cross
section, in square, hexagonal, or other packing. The contact area of the
smaller protrusions 40 is maximized while simultaneously leaving the
smaller channels 42 to form an open linked network. The larger
protrusions 46 are separated by larger drainage channels 48 in
communication with the smaller drainage channels. In a preferred example,
the protrusions 40 have a size of 10 μm and a height of 3 μm. Other
dimensions are possible. FIG. 5C shows protrusions 40 approach the
substrate 51 in the presence of the third medium 41. FIG. 5D shows local
trapping of third medium 41 in shallow pockets between the protrusions 40
and the substrate 51. The size of the pockets 52 may be 80% of that of
the protrusions 40. The depth of the pockets 52 is proportional to the
square of the size of the protrusions 40. FIG. 5E shows molecules 43
attached to the substrate 51 and to the protrusion 40 within one of the
pockets. FIG. 5F shows interaction between the molecules 43 attached to
the substrate 51 and the molecules 43 attached to the protrusion 40
within one of the pockets. For molecular transfer and controlled
execution of a chemisorption reaction, a gap between the stamp 38 and the
surface 50 of the order of 2 nm is usually sufficient. According to an
experimentally determined ratio of 750 between protrusion size and gap
thickness, patterns having a size of 1.5 μm is suitable. The recesses
42 providing the drainage channels on the stamp 38 are mutually connected
to drain the third medium away into the larger channels 48. Different
protrusions 40 on the stamp 38 can transfer different molecules by
selective inking Sequential methods such as robotic pipetting, pin
spotting, or ink jet spotting may employed for such inking. Semi-parallel
methods related to fluidic networks are equally applicable.

[0057]Referring now to FIG. 7A, in another example of the second
embodiment, a stamp 52 has shallow elongate parallel channels 54 formed
therein. The channels 54 are separated by intervening walls 53. In
preparation for operation, the channels 54 are coated with particular
molecules 56. In operation, the channels 54 form active zones in which
molecules 56 on the stamps 52 are brought into proximity with molecules
56 on the surface 58 of a substrate 60 when the stamp 52 is brought into
contact with the substrate 60. The molecules 56 on the stamp 52 and the
substrate 60 interact within each channel 54 when the stamp 52 is in
contact with the substrate 60 in presence of a third medium 62. For
biomolecular interactions, the third medium 62 may be water or a water
based solution containing other solvents, buffer ions, nucleosides and/or
enzymes. The channels 54 define a layer of the third medium 62 with
sufficient thickness to allow performance of a biochemical process. The
stamp 52 is preferably made from a thin layer of elastic material to
provide large area molecular contact. An externally applied load is
applied such that any sagging induced is sufficiently small to provide a
substantially uniform gap thickness in each depression 54. The load can
be regulated to adjust the gap. Referring to FIG. 7B, if the load is too
small, the gap may be too large to permit interaction between the
molecules on the stamp 52 and molecules on the substrate 60. Similarly,
referring to FIG. 7C, if the load is too large, the stamp 60 may collapse
and gap may be too small to permit interaction between the molecules on
the stamp 52 and molecules on the substrate 60. Referring to FIG. 7D, in
a particularly preferred example, a stamp 60 is patterned via contact
lithography for producing a 25 mm biochip. The channels 54 are 4 μm
wide and the separating walls 53 are 60 μm long, 1 μm wide, and 25
nm high. Excess third medium 62 displaced during printing is collected by
40-μm-wide and 40-μm-deep drainage channels 57 and drained away on
a macroscopic scale by several millimeters. The drainage channels 57
define active zones of the stamp occupied by groups of the smaller
channels 54. The desired channel height depends on the molecules involved
and can vary from e.g., 2 nm to 200 nm. In general, if the molecular
length is 20 nm then a channel of >20 nm is too large and a channel of
<5 nm is too small. The drainage channels 57 permit printing of a
relatively large substrate 60 without limiting effective fill factor. The
stamp 52 may be molded in Sylgard® 184 from a master with a
compression modulus of 3 Mpa. The master may be fabricated via
lithography methods such as projection lithography and e-beam
lithography. Such a stamp 52 may be pressed onto the surface 58 with an
average pressure of around 3 kPa distributed over the area of the stamp
52. In this example, drainage may require around 10 seconds, during which
the larger channels guide 57 away the third medium over around 70 mm.
FIG. 8A shows the height profile across a 4-μm-wide and initially 25
nm high channel 54 molded in Sylgard® 184 with a compression modulus
of 3 Mpa. The channel 54 was placed in contact with a substrate 60 under
3000 Pa pressure. The channel 54 is compressed to 22 nm at the edges and
to 18 nm in the center. A±10% gap width accuracy is achieved. This is
consistent with the length tolerance for hybridization on oligomers. To
tune the stamp 52 to a different system of molecular interaction, the
width of the channel 54 can be adjusted by changing the load. A reduction
of the load to 1500 Pa, for example, increases the minimal channel width
from 18 to 22 nm. In a second example, the stamp 52 comprises 10×10
μm sized active zones each having 6 12 μm long 200 nm wide and 25
nm high supporting walls 53 separating 1800 nm wide shallow channels 54.
8 μm deep and 8 μm wide drainage channels 57 direct excess third
medium such as water to the boundary of the stamp 52 around±10 mm
away. The stamp 52 may again be molded from Sylgard® 184 with a
Young's modulus of 3 MPa and pressed onto the surface with an average
pressure of 5 kPa distributed over the stamp 52. The time needed to
displace excess water to the boundary with the selected pressure may be
again around 10 seconds. FIG. 8B shows a height profile across such a
1800 nm wide and initially 25 nm high channel 54. In some embodiments of
the present invention, materials other than Sylgard® 184 and possibly
harder may be used.

[0058]Referring now to FIG. 9, in another embodiment of the present
invention, a bonding pad 68 comprises flat elastomeric adhesive
protrusions 70 separated by drainage channels 72. The channels 72 permit
a third medium such as air to escape when a flat object 74 is placed on
the pad 68 at high speed. At high speed, a pressure of greater than 1 bar
builds up in the third medium at a gap height of 0.2 μm or more. The
protrusions 70 extend from an elastomeric layer 76 supported by a
backplane 78. The elastomeric layer 76 may be a siloxane rubber such as
poly(dimethylsiloxane). This material relaxes to its original shape after
release of mechanical stress. The natural adhesive proprieties of the
surface may be enhanced with adhesives or other surface activation. The
backplane 78 is a flat layer such as thin glass, metal, silicon or
polymer, holding the elastomeric layer 76 accurately in place and
preventing lateral and vertical distortions. The pad 68 accurately holds
the parts 74 in place in a coplanar fashion to allow accurate robotic
transfer of the parts 74 to a carrier substrate or to allow parallel
processing of the parts 74. Removal of the parts 74 from the pad 68 is
typically performed by peeling to avoid potential overloading of the
parts 74 or the pad 68. Such overloading may occur in other separation
techniques such as, for example, vertical pulling. An example application
is thin film head slider fabrication. Present sliders 74 have typical
dimensions of 1×1 mm2 and can be accurately placed onto a
substrate by robot at vertical speeds of 10 mm/s. Accurate results are
achieved with elastomeric protrusions 70 of 10 to 20 μm width and
separated by drainage channels 76 of typically 1-5 μm diameter. The
channels 76 prevent trapping of air pockets between the sliders 74 and
the pad 76 by allowing air to escape. Air pressure remains moderate,
exceeding 1 bar only at distances closer than 150 nm. Stamp deformation
is low. The trapped air is negligible and any residual air can be quickly
dissipated through the pad 68. Elastomeric silicone rubbers are
surprisingly permeable for small amounts of gases. Without the drainage
channels 76, a pressure of greater than 1 bar builds up when a slider 74
approaches the pad 68 closer than 2 μm. Air pockets are then trapped
under the slider 74. The air pockets distort the pad 68 in an
unpredictable way and create vertical and/or lateral distortions.

[0059]Controlled layers of water are important in offset printing
processes for reliable print contrast. Dedicated topographic patterns
improve control over ink buffering, water buffering and tangential
transport of liquid. To maintain print contrast, it is desirable to avoid
longer distance net transport. FIG. 10A shows an side view of a typical
surface 80 of a printing cylinder 82 with random roughening. FIG. 10B is
a section through a micro structured surface 84 in which percolation
paths 86 are disposed. With the advent of low-cost micro structuring,
printing processes can be made more efficient by exchanging random
roughening for well defined structures. The well defined micro structures
optimize tangential and axial flow without reducing fill factor. This, is
especially important for printing operations onto impermeable surfaces
such as metal, glass, or ceramic where excess liquid cannot penetrate or
otherwise escape the printing gap.

[0060]Topographic patterns like those herein before described provide
improved control over ink buffering, water buffering and tangential
transport of liquid. In a preferred embodiment of the present invention,
small trenches are formed in one of the contact surfaces to create a
connected fluid mesh. The mesh permits high printing speeds, allows
larger parameter ranges for inking, allows thicker printed layers,
reduces dependency of color mixing on printed patterns, and simplifies
damping and inking. Topographic patterns for controlled water flow are
important in flat printing such as biochip patterning and also in
printing from stamps wrapped onto cylinders to form rolling contacts.
FIG. 11A shows flow resistance of fluid escaping a smooth advancing
cylinder 88. The resistance is represented by the large arrow 90. This
resistance generates pressure. The pressure lifts the cylinder 88 in a
similar manner to aqua planing of car tires. FIG. 11B shows that an
advancing cylinder 92 having a circumferentially disposed drainage
pattern 94 creates a smaller pressure in the liquid as indicated by the
smaller arrow 96. The cylinder 92 is thus less susceptible to aqua
planing. Thus, faster printing speeds can be achieved. In a rolling
contact, the third medium is displaced ahead of the cylinder or laterally
if there is excess medium only partially along the cylinder. The right
half of FIG. 11 shows the gap between the cylinder surface and the
substrate 89 as a function of the distance from the cylinder axis and its
tangential approximation. In FIG. 11A, the fluid resistance is high
because the remaining gap is small. In FIG. 11B, the fluid resistance is
smaller because of channels 94 formed in the surface of the cylinder 92.

[0061]In another embodiment of the present invention, self-assembly of
micrometer sized particles 110 using specific molecular interaction
involves patterning of either a substrate surface 111 or contacting
surface 112 of the particles 110 with structures herein before described.
The patterned contact surfaces 112 improve the binding speed. In
addition, the patterned contact surfaces 112 allow faster separation of
unbound or partially bound particles 110. This improves overall speed of
self-assembly process and improves specificity of interaction over
particles 113 with no patterned surface 112. FIG. 12A shows particles 110
having a patterned surface 112 interacting specifically with a surface
111. In FIG. 12B, there is shown a slower and less specific interaction
between the surface 111 and particles 113 without a patterned surface.
The receiving surface 111 can be patterned instead of the particles 110.